1. Field of the Invention
The present invention relates to a valve timing adjusting apparatus that adjusts valve timing of at least one of an intake valve and an exhaust valve of an internal combustion engine that are opened and closed by a camshaft upon transmission of a torque from a crankshaft.
2. Description of Related Art
In one known valve timing adjusting apparatus, the valve timing is adjusted by changing a relative rotational phase between two rotatable bodies, which are rotated synchronously with the crankshaft and the camshaft, respectively. For example, DE4110195C2 discloses a valve timing adjusting apparatus, which changes a relative rotational phase between two rotatable bodies through use of a differential gear mechanism, which includes a planet gear as its main component. Specifically, in the apparatus of DE4110195C2, two inner gears are provided to the rotatable body synchronized with the crankshaft and the rotatable body synchronized with the camshaft, respectively, and axial extents of these two inner gears do not overlap with each other. These inner gears are meshed with two outer gears, respectively, of the planet gear. In this way, a large speed reducing ratio can be obtained with the compact design.
In the apparatus disclosed in DE4110195C2, an inner peripheral wall of the crankshaft side rotatable body, which is rotated synchronously with the crankshaft, is engaged with an outer peripheral wall of the camshaft, so that the crankshaft side rotatable body is supported by the camshaft from a radially inner side of the crankshaft side rotatable body. In the above structure, an appropriate clearance should be provided between the crankshaft side rotatable body and the camshaft to permit the relative rotation between the crankshaft side rotatable body and the camshaft.
However, in the apparatus disclosed in DE4110195C2, the support position of the crankshaft side rotatable body by the camshaft is axially spaced from the inner gear of the camshaft side rotatable body, which is rotated synchronously with the camshaft. In the case of the above supporting structure, when the gravity is applied to the differential gear mechanism, in which the inner gear of the camshaft side rotatable body and the inner gear of the crankshaft side rotatable body are connected with one another through the planet gear, the crankshaft side rotatable body is tilted relative to the camshaft by the amount that corresponds to the clearance between the crankshaft side rotatable body and the camshaft. In this case, the crankshaft side rotatable body is locally engaged with the camshaft, so that wearing and seizing between the crankshaft side rotatable body and the camshaft are likely to occur. Furthermore, in the above supporting structure, when an oscillating torque of the camshaft is transmitted to the differential gear mechanism, the crankshaft side rotatable body is wobbled by the amount that corresponds to the clearance between the crankshaft side rotatable body and the camshaft. In this case, the crankshaft side rotatable body is wobbled relative to the camshaft, so that noise and a damage could possibly occur.